1. Technical Field
The present disclosure relates generally to circulatory support systems, and, more particularly, to a circulatory support system to provide partial or total bypass of the heart. The present disclosure is further directed to an axial flow pump and a portable microprocessor-based controller each being adapted for use in the circulatory support system.
2. Background of the Related Art
Mechanical blood pumps are commonly utilized to temporarily support or substitute the pumping function of the heart during heart surgery or during periods of heart failure. The most widely applied blood pumps include roller pumps and centrifugal pumps. Typically, these pumps are a component of a cardiopulmonary bypass system (e.g., a heart-lung machine) which includes an oxygenator, a heat exchanger, blood reservoirs and filters, and tubing which transports the blood from the patient through the bypass system and back to the patient. With these systems, blood is withdrawn from the patient via uptake cannula positioned within the vena cavae and atria or ventricles of the heart and pumped back into the pulmonary artery and aorta via a return cannula.
Although the aforedescribed cardiopulmonary bypass systems have been generally effective for their intended purposes, these systems are subject to certain disadvantages which detract from their usefulness. In particular, conventional bypass systems are relatively complicated and expensive to manufacture, expose the blood to a high surface area of foreign materials which may damage the blood, require full anticoagulation and cooling of the heart, and require considerable set up time and continual management by a skilled technician. These systems also require mechanical oxygenation of the blood which can have adverse affects on the patient.
U.S. Pat. No. 4,610,656 to Mortensen/Mehealus Partnership discloses a semi-automatic heart-lung substitution system. The Mortensen ""656 system includes a roller pump which pumps blood from the patient""s right heart via a venous cannula to a membrane oxygenator connected at the output of the roller pump. From the oxygenator, the blood flows to a compliance reservoir which is connected to a pulsatile left heart pump. Blood is pumped by the pulsatile left heart pump through a filter and bubble trap and then returned to the patient""s arterial system through an arterial cannula. The Mortensen ""656 system, however, is also a relatively complex device including several pumps and an oxygenator and, consequently, requires attendance of skilled technicians for set-up and operation.
Accordingly, the present disclosure is directed to a circulatory support system to support the functioning of the heart. In a preferred embodiment, the support system includes an extracorporeal pump member having a pump housing dimensioned for positioning directly on or adjacent to the chest area of a patient and defining inlet and outlet ports, a rotating member rotatably mounted in the pump housing to impart mechanical energy to blood entering the inlet port and to direct the blood through the outlet port, an inlet cannulated tube connected to the inlet port of the pump housing and having an inlet open end portion dimensioned for insertion within the patient""s heart whereby blood is drawn from the heart through the inlet cannulated tube and directed into the pump housing, and an outlet cannulated tube connected to the outlet port of the pump housing and having an outlet end portion dimensioned for insertion within a major blood vessel associated with the heart whereby blood exiting the outlet port of the pump housing is conveyed through the outlet cannulated tube into the major blood vessel for transfer by the arterial system of the patient.
The support system is particularly contemplated for left heart bypass while the right heart functions to direct blood to the lungs. It is envisioned that the right heart may be slowed or even stopped while the support system is utilized for left heart bypass.
A method for providing at least partial bypass of the heart to supplement the pumping function of the heart to thereby enable the surgeon to perform various surgical procedures thereon is also disclosed. The method includes the steps of providing a circulatory assist system having a portable extracorporeal axial flow pump with a pump housing and inlet and outlet ports, a rotating pumping member disposed in the pump housing and inlet and outlet cannulated tubes respectively connected to the inlet and outlet ports of the pump housing, accessing the patient""s left ventricle of the heart with the inlet cannulated tube, accessing the aorta with the outlet cannulated tube, actuating the rotating pumping member to draw oxygenated blood from the left ventricle of the heart through the lumen of the inlet cannulated tube and into the inlet port of the pump housing whereby the pumping member imparts mechanical energy to the oxygenated blood passing through the pump housing and directs the oxygenated blood through the outlet port and through the lumen of the outlet cannulated tube to be transferred by the aorta to the systemic arteries, and permitting blood returning through the systemic veins to the right atrium to be directed through the right ventricle to the patient""s lungs for oxygenation and subsequent pulmonary circulation. The left ventricle may be accessed through the heart wall, mitral valve or aortic valve. In an alternate embodiment, a second circulatory assist system may be utilized to facilitate the pumping function of the right side of the heart.
The present disclosure is further directed to a pump to be used in the circulatory support system. The pump includes a pump housing including an inlet end portion defining an inlet port for permitting blood to enter the pump housing and an outlet end portion defining an outlet port for permitting blood to exit the pump housing. The inlet and outlet end portions preferably each have central hub portions with straightener blades extending therefrom for facilitating passage of blood through the pump housing. A rotatable member is mounted for rotational movement to the central hub portions of the pump housing. The rotatable member includes at least one impeller blade for imparting pump energy to blood passing through the pump housing and a magnetically actuated rotor. A motor stator is disposed in the pump housing and has at least one stator blade extending from an inner surface thereof. The one stator blade and the one impeller blade of the rotatable member are cooperatively configured to exert a substantially axial flow pumping energy to blood flowing along the blood path. Preferably, the one impeller blade and the one stator blade each extend axially and peripherally within the pump housing.
The present disclosure is further directed to a control unit to be used in the circulatory support system. In an exemplary embodiment, the control unit includes circuitry for supplying power to the flow pump to cause the pump to rotate, and circuitry responsive to a pressure sense signal from a pressure transducer located on the inlet side of the pump (e.g., within the atrium), for commanding a reduction in motor speed to a lower speed when the pressure is determined to be below a predetermined threshold. The control unit preferably also includes circuitry responsive to a bubble sense signal provided by a bubble detector mounted to one of the cannulas, for generating a bubble alarm and for causing rotation of the pump to cease if the bubble sense signal indicates the presence of an air bubble. The control unit may further include circuitry responsive to the bubble sense signal indicating the presence of an air bubble for causing a clamping device mounted to one of the cannulas to clamp down on the cannula to prevent air from entering the patient""s bloodstream.